Post-collisional alkaline lamprophyre magmatism in northern Iran: Implications from whole-rock geochemistry and mineral compositions

IF 1 4区 地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY Island Arc Pub Date : 2022-10-21 DOI:10.1111/iar.12469
Hadi Omrani, Christina Günter, Gholam Hossein Shamanian, Mehdi Omrani
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引用次数: 2

Abstract

The Shanderman lamprophyre dykes crop out in the western part of the Alborz Mountains (Talesh). These rocks are classified as camptonites, composed of primary olivine, Ti-rich diopside, kaersutite, biotite, plagioclase, K–feldspar, and minor Ti–rich spinels, magnetite, pentlandite–pyrrhotite/chalcopyrite, and powellite–scheelite. Secondary analcime–wairakite, serpentines, and prehnite are common minor minerals within the studied rocks. Olivine, Ti-rich diopside, spinel, and amphibole show distinct chemical zoning. Spinels display a core-to-rim decrease in Cr2O3, MgO, and Al2O3 concentrations and an increase in TiO2 and FeOT (total Fe as FeO), reflecting the oxidation state increase due to hydrothermal fluid influx. Low SiO2 contents (<42 wt%), high MgO (12.44 to 13.98 wt%), and Fe2O3T (12.76 to 13.43 wt%), Cr (318–537 μg/g) and Ni (231–327 μg/g) contents indicate the ultrabasic nature of the rocks. The samples show potassic character (2.1–2.8 wt% K2O), along with elevated LREE and LILE, and also exhibit minor positive Eu anomalies (Eu/Eu* = 1.09 to 1.20). Olivine–spinel geothermometry indicates a maximum crystallization temperature of 1227 °C (ave. 988 °C ± 65 °C). Exsolution of pentlandite–pyrrhotite/chalcopyrite solid solutions occurred during magma cooling and crystallization. At lower temperatures, analcime–wairakite and prehnite partially replaced plagioclases. The geochemical modeling of the rocks indicates the Shanderman lamprophyre magmas were derived from low-grade melting (<5%) of amphibole–bearing garnet lherzolite source without or with very few phlogopites. The primary magma of Shanderman lamprophyres was derived from a depth of ~135 km by partial melting of a metasomatized mantle source in a post-collisional environment.

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伊朗北部碰撞后碱性煌斑岩岩浆作用:全岩地球化学和矿物组成的意义
山德曼煌斑岩岩脉在阿尔布尔斯山脉(Talesh)西部突现。这些岩石被分类为营长岩,由原生橄榄石、富钛透辉石、克尔长岩、黑云母、斜长石、钾长石和少量富钛尖晶石、磁铁矿、辉黄铁矿/黄铜矿和白钨矿组成。次生白拉石、蛇纹石、前辉石是研究岩石中常见的小矿物。橄榄石、富钛透辉石、尖晶石、角闪石具有明显的化学分带。尖晶石中Cr2O3、MgO和Al2O3含量从核心到边缘呈下降趋势,TiO2和FeOT(总Fe为FeO)含量呈上升趋势,反映了热液流入导致氧化态升高。低SiO2 (<42 wt%)、高MgO (12.44 ~ 13.98 wt%)、高Fe2O3T (12.76 ~ 13.43 wt%)、高Cr (318 ~ 537 μg/g)、高Ni (231 ~ 327 μg/g)含量表明岩石具有超基性。样品显示钾质特征(2.1-2.8 wt% K2O),同时LREE和LILE升高,并且还表现出轻微的正Eu异常(Eu/Eu* = 1.09 ~ 1.20)。橄榄石-尖晶石的地热测量表明,最高结晶温度为1227°C(最低温度为988°C±65°C)。岩浆冷却结晶过程中出现了硫铁矿-磁黄铁矿/黄铜矿固溶体的析出。在较低的温度下,斜长石部分取代了斜长石。岩石地球化学模拟表明,山德曼煌斑岩岩浆来源于含角闪石的石榴石-辉橄榄岩低品位熔融(<5%)源,无或极少量辉云母。山德曼煌斑岩的原始岩浆来自于碰撞后环境中交代地幔源的部分熔融作用,岩浆深度约135 km。
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来源期刊
Island Arc
Island Arc 地学-地球科学综合
CiteScore
2.90
自引率
26.70%
发文量
32
审稿时长
>12 weeks
期刊介绍: Island Arc is the official journal of the Geological Society of Japan. This journal focuses on the structure, dynamics and evolution of convergent plate boundaries, including trenches, volcanic arcs, subducting plates, and both accretionary and collisional orogens in modern and ancient settings. The Journal also opens to other key geological processes and features of broad interest such as oceanic basins, mid-ocean ridges, hot spots, continental cratons, and their surfaces and roots. Papers that discuss the interaction between solid earth, atmosphere, and bodies of water are also welcome. Articles of immediate importance to other researchers, either by virtue of their new data, results or ideas are given priority publication. Island Arc publishes peer-reviewed articles and reviews. Original scientific articles, of a maximum length of 15 printed pages, are published promptly with a standard publication time from submission of 3 months. All articles are peer reviewed by at least two research experts in the field of the submitted paper.
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